A. Spermatogenesis Inhibitors
The prevention of unplanned pregnancy in humans and other mammals is of continuing concern for both the developing and the developed world. A variety of methods and products have been proposed or developed for the prevention of pregnancy. These products include: surgical sterilization, condoms, birth control pills containing progestin or a combination of progestin and estrogen, subdermal implants containing delayed release forms of progesterone, intrauterine devices, spermicidal creams or gels, and intravaginal barriers such as sponges or diaphragms.
Male contraceptive approaches have included the barrier methods, hormonal methods, the rhythm method, and immunological methods. More recently, researchers have begun investigating compounds which inhibit spermatogenesis by disrupting junctional complex sites between Sertoli cells and germ cells in the testes. One such compound is lonidamine (1-(2,4,-dichlorobenzyl)-1H-indazole-3-carboxylic acid). Lonidamine belongs to a group of indazole-carboxylic acid compounds that was found to be a potent inhibitor of spermatogenesis. However, the antispermatogenic effects of lonidamine at high doses were found to be irreversible and toxic. See generally Lonidamine: A New Pharmacological Approach to the Study and Control of Spermatogenesis and Tumors, Chemotherapy, 27 Suppl. 2, 1-120 (1981a 1981b); Lonidamine, Proceedings of the 2nd International Symposium, Vancouver (1982).
Several analogues of lonidamine have recently been investigated as spermatogenic inhibitors. See Silvestrini et al., U.S. Pat. No. 6,001,865; Baiocchi et al., U.S. Pat. No. 5,112,986; Silvestrini, U.S. Pat. No. 4,282,237; Palazzo et al., U.S. Pat. No. 3,895,026; Cheng et al., Two New Male Contraceptives Exert Their Effects by Depleting Germ Cells Prematurely from the Testis, BIOLOGY OF REPRODUCTION 65, 449-461 (2001); Grima et al., Reversible Inhibition of Spermatogenesis in Rats Using a New Male Contraceptive 1-(2,4-dichlorobenzyl)-indazole-3-carbohydrazide, BIOLOGY OF REPRODUCTION 64, 1500-1508 (2001); Corsi et al., 1-Halobenzyl-1H-indazole-3-carboxylic acids: A New Class of Antispermatogenic Agents, J. MED. CHEM., Vol. 19, No. 6, 778-783 (1976); Palazzo et al., Synthesis and pharmacological properties of 1-substituted 3-dimethylaminoalkoxy-1H-indazoles, J. MED. CHEM. Vol. 9, 38-41 (1966). Despite these advances, there remains a need for compounds which are antispermatogenic but preferably do not exhibit toxic side effects.
It is contemplated that some of the compounds of the present invention interact either directly or indirectly with elongation factor 1 alpha (EF1α). As background, EF1α plays a critical role in amino acid addition to the growing peptide chain during protein synthesis by the ribosome. Specifically EF1α and EF1β are involved in recruitment of amino acyl-tRNAs to the ribosome.
The somatic form of eEF-1 alpha (eEF-1 alpha S) mRNA is virtually undetectable in male and female germ cells of the adult gonad but is very abundant in embryonic cells after the neurula stage. In contrast, another form of eEF-1 alpha (eEF-1 alpha O) mRNA is highly concentrated in oogonia and in previtellogenic oocytes but is undetectable in eggs and embryos. eEF-1 alpha O mRNA is also present in spermatogonia and spermatocytes of adult testis. The latter finding identifies eEF-1 alpha O mRNA as a germ cell-specific gene product. Although germ cells contain very little eEF-1 alpha S mRNA, several eEF-1 alpha S retropseudogenes exist in X. laevis chromosomes. These genes are thought to arise in germ cells from reverse transcription of mRNA and subsequent integration of the cDNA copies into chromosomal DNA. It is suggested that eEF-1 alpha S pseudogenes are generated in primordial germ cells of the embryo before they differentiate into oogonia or spermatogonia. See Abdallah et al., Germ cell-specific expression of a gene encoding eukaryotic translation elongation factor 1 alpha (eEF-1 alpha) and generation of eEF-1 alpha retropseudogenes in Xenopus laevis, Proc. Natl. Acad. Sci. U.S.A 88: 9277-9281 (1991).
Protein synthesis is believed to be under control of the cell cycle during meiosis and mitosis. Any relationship between substrates for cdc2 kinase and components of the protein synthetic apparatus would therefore be of prime importance. During meiosis of Xenopus laevis oocytes one of the substrates for this kinase is a p47 protein, which is complexed to two other proteins, P36 and P30. Judged from partial amino acid sequence data on P47 and P30, the P30 and P47 proteins were reported to resemble the protein synthetic elongation factors (EF) 1 beta and 1 gamma from Artemia salina. See Belle et al., A purified complex from Xenopus oocytes contains a p47 protein, an in vivo substrate of MPF, and a p30 protein respectively homologous to elongation factors EF-1 gamma and EF-1 beta. FEBS Lett. 255: 101-104 (1989). This paper shows that the complex composed of P30, P47, and P36 from Xenopus is identical to the complex of EF-1 beta, EF-1 gamma, and EF-1 delta from Artemia according to two criteria. 1) Both stimulate elongation factor 1 alpha-mediated transfer RNA binding to ribosomes and exchange of guanine nucleotides on elongation factor 1 alpha to a comparable degree. 2) Each of the three subunits of the protein complex P30.P47.P36 from Xenopus shows a structural homology with one of the corresponding subunits of EF-1 beta gamma delta from Artemia. Presumably the phosphorylation of EF-1 gamma, which associates with tubulin at least in vitro, is important in processes following the onset of meiosis which is accompanied by a rise of protein synthesis. See Janssen et al., A major substrate of maturation promoting factor identified as elongation factor 1 beta gamma delta in Xenopus laevis. J. Biol. Chem. 266: 14885-14888 (1991).
Thus, in the present invention, it is conceivable that inhibitors of the testis-specific isoform of EF1-alpha could disrupt spermatogenesis.
B. Anti-Cancer Agents
There is a pronounced need for safe and more efficacious anti-tumor agents. While a wide variety of chemotherapeutic agents are presently used for the treatment, suppression and prevention of tumors, tumors may develop a resistance to such agents, especially highly malignant or solid tumors. Thus, tumor relapse is a common problem. Also, existing agents, even if effective, may be inconvenient to administer in effective dosages and have inadequate therapeutic indexes. Thus, patients may suffer from pain and other side-effects of their administration, especially from the administration of high doses of anti-tumor agents with relatively low potencies. It is contemplated that some of the compounds of the present invention are useful in cancer treatment.
It is contemplated that some of the compounds of the present invention exert their anti-cancer effects by binding either directly or indirectly to heat shock proteins. In recent years, heat shock 90 proteins (“Hsp90”), the molecular chaperones responsible for protein folding and maturation in vivo and which have been found at higher levels in cancerous cells than in normal cells.
The 90 kDa heat shock proteins belong to a family of chaperones that regulate intracellular functions and are required for the refolding of denatured proteins following heat shock, as well as the conformational maturation of a large number of key proteins involved in cellular processes. In yeast, a homologue of Hsp90 with a slightly lower molecular weight at 83 kDa (Hsp83) serves an identical function. The Hsp90 family of chaperones is comprised of four different isoforms. Hsp90 α and Hsp90 β are found predominately in the cytosol, the 94 kDa glucose-regulated protein (“GRP94”) is localized to the endoplasmic reticulum, and Hsp75/tumour necrosis factor receptor associated protein 1 (“TRAP-1”) resides mainly in the mitochondrial matrix. These Hsp90s bind to client proteins in the presence of cochaperones, immunophilins, and partner proteins to make the multiprotein complex responsible for conformational maturation of newly formed nascent peptides into biologically active three-dimensional structures.
As discussed more fully below, Hsp90 is an ATP-dependent protein with an ATP binding site in the N-terminal region of the active homodimer. Disruption of the ATPase activity of Hsp90 results in the stabilization of multiprotein complexes and subsequent ubiquitination of the client protein, which undergoes proteasome-mediated hydrolysis.
More specifically, in an ATP-dependent fashion, Hsp70 binds to newly synthesized proteins cotranslationally and/or posttranslationally to stabilize the nascent peptide by preventing aggregation. Stabilization of the Hsp70/polypeptide binary complex is dependent upon the binding of Hsp70 interacting protein (“HIP”), which occurs after Hsp70 binds to the newly formed peptide. Hsp70-Hsp90 organizing protein (“HOP”) contains highly conserved TPRs (tetratricopeptide repeats) that are recognized by both Hsp70 and Hsp90, promoting the union of Hsp70/HIP and Hsp90, which results in a heteroprotein complex. In the case of telomerase and steroid hormone receptors, the client protein is transferred from the Hsp70 system to the Hsp90 homodimer with concomitant release of Hsp70, HIP, and HOP. Upon binding of ATP and an immunophilin with cis/trans prolyl-isomerase activity (FKBP51, FKBP-52, or CyP A), the ensemble folds the client protein into its three-dimensional structure. In a subsequent event, p23 binds Hsp90 near the N-terminal region promoting the hydrolysis of ATP and release of the folded protein Hsp90 partner proteins, and ADP.
EXAMPLEs of proteins dependent upon Hsp90 for conformational maturation include: oncogenic Src kinase, Raf, p185, mutant p53 (not normal p53), telomerase, steroid hormone receptors, polo-like kinase (“PLK”), protein kinase B (“AKT”), death domain kinase (“RIP”), MET kinase, focal adhesion kinase (“FAK”), aryl hydrocarbon receptor, RNA-dependent protein kinase (“PKR”), nitric oxide synthase (“NOS”), centrosomal proteins, and others. In addition, other proteins, such as cyclin dependent kinase 4 (“CDK4”), cyclin dependent kinase 6 (“CDK6”), and human epidermal growth factor receptor 2 (“Her-2”) are thought to be client proteins of Hsp90. Of these Hsp90 client proteins, Raf, PLK, RIP, AKT, FAK, telomerase, and MET kinase are directly associated with the six hallmarks of cancer: (1) self-sufficiency in growth signals; (2) sensitivity to antigrowth signals; (3) evasion of apoptosis; (4) unlimited replication potential; (5) sustained angiogenesis; and (6) tissue invasion/metastasis. Consequently, Hsp90 inhibition is a target for the development of cancer therapeutics because multiple signaling pathways can be simultaneously inhibited by disruption of the Hsp90 protein folding machinery.
Known inhibitors of Hsp90 include the anti-tumor antibiotics geldanamycin (“GDA”), radicicol (“RDC”), herbimycin A (“HB”), a 17-allylamino derivative of GDA (“17-AAG”), and the synthetic ATP analog called PU3. These molecules exert their activity by binding to the N-terminal ATP binding pocket and inhibit the ATPase activity of Hsp90. Novobiocin (a DNA gyrase ATP binding site inhibitor) has been found to selectively bind to the C-terminal domain of Hsp90. In all cases, these complex structures, however, are very difficult to isolate and/or synthesize. As such, there remains a need to develop other Hsp90 inhibitors useful as anti-cancer agents. Most preferably, these new Hsp90 inhibitors have decreased toxicity, increased solubility, and/or increased selectivity for Hsp90. These Hsp90 inhibitors may operate by binding to the N-terminal region, the C-terminal region, or another region of the homodimer that causes a conformational change.